Random access method considering a coverage level, subcarrier spacing configuration and/or multi-tone configuration in internet of things environment

ABSTRACT

Provided is random access method, performed by terminal for uplink data transmission during random access process between cellular based machine communication terminal and base station. The method includes performing random access process between cellular based machine communication terminal and base station, and the random access process includes selecting random access resource by considering coverage level and whether to support multi-tone transmission or not. Terminal can perform efficient random access process in response to coverage level, subcarrier spacing configuration, multi-tone configuration when machine communication terminal or machine communication device which operates in cellular based IoT system perform random access, number of repetition may be increased, when coverage level is changed, by minimizing the change in coverage level, and operation time of the terminal, due to standing by up to PRACH resource corresponding to the coverage level, may be reduced to reduce energy consumption and to enhance delay time performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/591,704 filed on Oct. 3, 2019, which is a Continuation Application ofU.S. patent application Ser. No. 15/524,466 Filed on May 4, 2017, whichclaims the benefit under 35 USC 119(a) of PCT Application No.PCT/KR2017/000939, filed on Jan. 26, 2017, which claims the benefit ofKorean Patent Application No. 10-2016-0011893 filed Jan. 29, 2016,Korean Patent Application No. 10-2016-0025783 filed on Mar. 3, 2016, andKorean Patent Application No. 10-2016-0043317 filed on Apr. 8, 2016,Korean Patent Application No. 10-2016-0058374 filed on May 12, 2016, andKorean Patent Application No. 10-2016-0154109 filed on Nov. 18, 2016 inthe Korean Intellectual Property Office, the entire disclosure of whichis incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to methods for performing a random accessin a machine communication terminal or a machine communication device,and more particularly, to methods for efficiently select a preamble andperforming a random access when a machine communication terminal or amachine communication device in a cellular based Internet of Things(IoT) environment continuously fails to perform a random access process.

Related Art

A cellular based IoT system for implementing an Internet of Thingsenvironment, aims at providing reliable connection based on widecoverage in a licensed band in order to provide services to massiveterminals, for example, machine communication terminals or machinecommunication devices.

As an example of the cellular based IoT system, narrow band-IoT (NB-IoT)provides an IoT service suitable for a sensor-centered application atlow-speed data rate by using a bandwidth smaller than a bandwidth of 1.4MHz of machine type communication (MTC), that is, a bandwidth smallerthan the bandwidth 1.4 MHz in both uplink and downlink, for example, 180kHz.

In the NB-IoT, OFDMA is used in the downlink and a very small subcarrierspacing, for example, a 15-kHz subcarrier spacing may be used.

In the NB-IoT uplink, SC-FDMA may be used. In the NB-IoT uplink, a3.75-kHz subcarrier spacing or the 15-kHz subcarrier spacing may beused.

A random access as a procedure for a kind of data transmission in whichthe terminal transmits data to a base station at a predetermined timefor connection to the base station and data transmission by the terminalserves to start communication which starts in all terminals. Inparticular, a method is requested, in which the base station maysuccessfully receive a signal during the random access process, which istransmitted from a terminal which is very far away, in which coverage of20 dB or more is extended in order to reflect an NB-IoT servicecharacteristic requiring a wide coverage area and may also successfullytransmit a response signal to the received signal to the correspondingterminal in a long distance.

When SC-FDMA based uplink of the NB-IoT is designed, a design of aphysical random access channel (PRACH) needs to be modified in order toperform an LTE random access procedure due to the reduced bandwidth ofthe NB-IoT and the modification may partially influence the LTE randomaccess procedure.

The LTE random access is used for multiple purposes such as an initialaccess and a scheduling request at the time of configuring a radio linkand a primary purpose of the random access is to prepare for the datatransmission by achieving uplink synchronization. The random access maybecome a contention-based random access or a contention-free randomaccess.

SUMMARY OF THE INVENTION

In the cellular based IoT system, for example, a Narrow band-Internet ofThings (NB-IoT) system, a scheme is considered, which divisionallyprovides the service separately in a plurality of coverage classes (CCs)or coverage levels (CLs) according to a channel state of the terminal.The coverage classes (CCs) or the coverage levels (CLs) are generallyclassified into normal coverage (hereinafter, referred to as CC1 orCL1), robust coverage (hereinafter, referred to as CC2 or CL2), andextreme coverage (hereinafter, CC3 or CL3) and the base station allowsthe terminals which belong to each coverage class (CC) or coverage level(CL) to receive an optimized service according to the channel state bydifferentiating parameters, such as locations of resources used by theterminal, the number of repetition transmission, a modulation and codingscheme (MCS), and the like according to the coverage class (CC) or thecoverage level (CL).

Further, the NB-IoT may define three configurations according to thesubcarrier spacing and/or whether to support multi-tone transmission ornot which the terminal uses during uplink transmission, and the NB-IoTmay support the defined coverage class or coverage level. Performancecharacteristics for respective subcarrier spacing configurations and/ormulti-tone configurations during the uplink transmission are shown inTable 1.

TABLE 1 3.75 kHz, single-tone Bad channel state, low transmission rate,and terminal positioned on the edge of a cell 15 kHz, single-toneIntermediate channel state, intermediate transmission rate, and terminalpositioned within a radius up to approximately 10 km from the center ofthe cell 15 kHz, multi-tone Good channel state, high transmission rate,terminal positioned at the center of the cell

During the random access process by the terminal in the existingdiscussed NB-IoT system, in the case of the failure, in the case where arandom access response (Message2) to transmission of a preamble(Message1) may not be received when the random access is performed inthe coverage class (CC) or coverage level (CL) selected by the terminal,or in the case where a Contention Resolution (Message4) which is aresponse to transmission of a connection request (Message3) may not bereceived, the random access process is reperformed and the preamble istransmitted again. In this case, when continuous preamble retransmissionoccurs at a predetermined number of times or more, the terminal performsthe random access again by changing the current coverage level (CC) orcoverage level (CL) to a coverage class (CC) or coverage level (CL)supporting the channel state which is lower by one level to prepare forthe data transmission. However, the procedure for reperforming therandom access after changing the coverage class (CC) or the coveragelevel (CL) has a problem that an operation time and an operation timesignificantly increase because the terminal needs to perform the randomaccess process in the corresponding PRACH at the increased number ofrepetition again from the beginning at the time of performing the randomaccess in the changed coverage class (CC) or coverage level.

Therefore, example embodiments of the present invention provide methodsfor sequentially using preamble resources in the random access processby considering performance for each level of a subcarrier spacing and/ormulti-tone configuration in each coverage class (CC) or coverage level(CL) in response to the subcarrier spacing and/or multi-toneconfiguration when the terminal performs the random access in thecellular IoT system, for example, the NB-IoT. In detail, exampleembodiments of the present invention provide methods for reperformingthe random access by changing the coverage class (CC) or the coveragelevel (CL) when the random access process fails by the terminal up tothe last step of the subcarrier spacing and/or multi-tone configurationprovided in the coverage class (CC) or the coverage level (CL) afterattempting retransmission by primarily changing subcarrier spacingand/or multi-tone configuration used in the coverage class (CC) or thecoverage level (CL) when selecting a resource for preamble transmissionwhile reperforming the random access when failing to transmitting aconnection request message Message3 for uplink data transmission duringthe random access process.

According to example embodiments of the present invention, provided isan efficient random access method considering a coverage class (CC) orcoverage level (CL) and an uplink subcarrier spacing and/or multi-toneconfiguration in a cellular based IoT system, for example, an NB-IoT.

Further, according to the example embodiments of the present invention,provided is a simplified data transmitting method that can reduce delaytime and energy consumption of terminals which transmit small data inthe cellular based IoT system.

In an aspect, a random access method, which is performed by theterminal, for uplink data transmission during a random access processbetween a cellular based machine communication terminal and a basestation is provided. The method includes: performing the random accessprocess between the cellular based machine communication terminal andthe base station and the random access process includes selecting arandom access resource by considering a coverage level and whether tosupport multi-tone transmission or not.

The selecting a random access resource by considering a coverage leveland whether to support a multi-tone transmission or not may includeselecting the random access resource by considering the selectedcoverage level and whether to support the multi-tone transmission or notwhen a message (Message3) is not yet transmitted, wherein the message(Message3) is a message for requesting a connection for the uplink datatransmission by the machine communication terminal.

The selecting the random access resource by considering the selectedcoverage level and whether to support the multi-tone transmission or notwhen the message (Message3)—the message (Message3) being the message forrequesting the connection for the uplink data transmission by themachine communication terminal—is not yet transmitted, may includeselecting the random access resource that uses another subcarrierspacing and/or multi-tone configuration used in a coverage level equalto the selected coverage level, when a failure of HARQ transmission ofthe message (Message3) occurs consecutively or unsuccessful receipt ofContention Resolution occurs consecutively and thus a number of preambletransmission is more than a maximum number of preamble transmission.

The selecting the random access resource by considering the coveragelevel and whether to support multi-tone transmission or not may includeselecting the random access resource corresponding to the selectedcoverage level and corresponding to the support of the multi-tonetransmission when the message (Message3)—the message (Message3) beingthe message for requesting the connection for the uplink datatransmission by the machine communication terminal—is not yettransmitted by the machine communication terminal.

In the selecting of the random access resource by considering theselected coverage level and whether to support the multi-tonetransmission or not when the message (Message3)—the message (Message3)being the message for requesting the connection for the uplink datatransmission by the machine communication terminal—is not yettransmitted by the machine communication terminal, the random accessresource using the multi-tone configuration transmission used in thecoverage level equal to the selected coverage level may be selected whenthe message (Message3) is not yet transmitted by the machinecommunication terminal.

The selecting of the random access resource by considering the selectedcoverage level and whether to support the multi-tone transmission or notwhen the message (Message3)—the message (Message3) being the message forrequesting the connection for the uplink data transmission by themachine communication terminal—is not yet transmitted by the machinecommunication terminal may include performing the random access bychanging the multi-tone configuration at the coverage level equal to theselected coverage level when the message (Message3) is not yettransmitted by the machine communication terminal.

In the selecting the random access resource by considering the selectedcoverage level and whether to support the multi-tone transmission or notwhen the message (Message3)—the message (Message3) being the message forrequesting the connection for the uplink data transmission by themachine communication terminal—is not yet transmitted by the machinecommunication terminal, the base station may stepwise set the radonaccess resource by considering the coverage level and the subcarrierspacing and/or multi-tone configuration and the machine communicationterminal may stepwise select the random access resource at the time ofperforming the random access when the message (Message3) is not yettransmitted by the machine communication terminal.

The performing of the random access by changing the subcarrier spacingand/or multi-tone configuration at the coverage level equal to theselected coverage level when the message (Message3)—the message(Message3) being the message for requesting the connection for theuplink data transmission by the machine communication terminal—is notyet transmitted by the machine communication terminal may includeperforming the random access by finally changing the selected coveragelevel when a last step of a combination of the subcarrier spacing and/ormulti-tone configuration provided in the selected coverage level isfailed after attempting the random access.

The coverage level may include normal coverage, robust coverage, andextreme coverage.

The random access process between the machine communication terminal andthe base station may be applied to cellular based narrowband machinecommunication.

The machine communication terminal may include a Narrowband-Internet ofThing (NB-IoT) terminal capable of accessing a radio access networkusing a channel bandwidth of 180 kHz.

Whether to support the multi-tone transmission may be whether to supportmulti-tone Message 3 transmission or not. The random access process mayfurther include selecting the coverage level by the machinecommunication terminal.

The case where the message (Message3)—the message (Message3) being themessage for requesting the connection for the uplink data transmissionby the machine communication terminal—is not yet transmitted mayrepresent a case where first random access preamble transmission isperformed by the machine communication terminal.

The random access process between the machine communication terminal andthe base station may include transmitting, by the machine communicationterminal, a random access preamble to the base station, receiving, bythe machine communication terminal, a random access response (RAR)message from the machine communication terminal, transmitting, by themachine communication terminal, the message (Message 3) to the basestation, the message (Message3) being the message for requesting theconnection for the uplink data transmission by the machine communicationterminal, and receiving, by the machine communication terminal,Contention Resolution for announcing that the Message 3 transmitted bythe machine communication terminal is received by the base station.

In another aspect, a machine communication terminal performing a randomaccess process for uplink data transmission with a base station usingcellular based machine communication, may include a transceivertransmitting or receiving a radio frequency signal to or from the basestation through an antenna, and a processor determining a time oftransmitting the radio frequency signal by controlling the transceiver,wherein the processor may process a step of performing the random accessprocess between the machine communication terminal and the base station,and wherein the random access process may include selecting a randomaccess resource by considering a coverage level and whether to supportmulti-tone transmission or not.

In yet another aspect, a machine communication device performing arandom access process for uplink data transmission with a base stationfor cellular based machine communication may include a transceivertransmitting or receiving a radio frequency signal to or from the basestation through an antenna, and a processor may determine the time oftransmitting the radio frequency signal by controlling the transceiver,wherein the processor may process performing the random access processbetween the machine communication device and the base station, and therandom access process may include selecting a random access resource byconsidering a coverage level and whether to support multi-tonetransmission.

In still yet another aspect, a random access method between a cellularbased machine communication terminal and abase station may includereceiving, by the base station, a random access preamble from themachine communication terminal, transmitting a random access response(RAR) message to the machine communication terminal, receiving, by thebase station, a message (Message 3) from the machine communicationterminal, wherein the message (Message3) is a message for requesting aconnection for the uplink data transmission, and transmitting, by thebase station, contention resolution (CR) to the machine communicationterminal, wherein the contention resolution (CR) indicates that theMessage 3 transmitted by the machine communication terminal is receivedby the base station, wherein, in the random access process, a randomaccess resource may be selected by considering a coverage level andwhether to support multi-tone transmission or not.

In still yet another aspect, a base station performing a random accessprocess for uplink data transmission with a cellular based machinecommunication terminal may include a transceiver transmitting orreceiving a radio frequency signal to or from the machine communicationterminal through an antenna, and a processor determining the time oftransmitting the radio frequency signal by controlling the transceiver,wherein the processor may process receiving a random access preamblefrom the machine communication terminal, transmitting a random accessresponse (RAR) message to the machine communication terminal, receivinga message (Message 3) from the machine communication terminal, themessage (Message3) being the message for requesting the connection forthe uplink data transmission, and transmitting Contention Resolution tothe machine communication terminal, wherein the contention resolution(CR) indicates that the Message 3 transmitted by the machinecommunication terminal is received by the base station, and wherein arandom access resource, in the random access process, may be selected byconsidering a coverage level and whether to support multi-tonetransmission or not.

In still yet another aspect, according to a small data transmissionsupporting method, the base station may broadcast system information(SI) or downlink control information (DCI) including a criterion fordetermining whether they are small data or not, and a terminal maydetermine whether they are the small data or not based on predefinedcriterion. Further, the base station may separately configure a randomaccess channel for a small data transmitting terminal and a randomaccess channel for a normal terminal and may transmit the DCI includingresource allocation information for uplink/downlink transmission. Eachterminal may transmit data having a predetermined size and operate in asleep mode until data to be transmitted is generated. The small datatransmission supporting method may be generally divided into a smalldata transmission request process and a small data transmission processof the terminal. When the terminal is initially powered on, the terminalmay generate the data to be transmitted. The terminal may first performsynchronization with the base station for data transmission and receivethe system information. The terminal may determine whether the smalldata may be transmitted or not through comparison with informationincluded in the system information or a previously defined value afterreceiving the system information. When the small data may betransmitted, the terminal may perform the random access for requestingtransmission of the small data and performs the small data transmissionprocess by a method optimized to transmission of the small data afterapproving the request.

The present invention provides a method in which a terminal can performan efficient random access process in response to a coverage class orcoverage level, a subcarrier spacing configuration and/or a multi-toneconfiguration when a machine communication terminal or a machinecommunication device which operates in a cellular based IoT systemperform a random access.

When a connection request message Message3 for performing uplink datatransmission during the random access process is not yet transmitted,the machine communication terminal or the machine communication devicemay select a PRACH resource and a preamble by considering the coverageclass (CC) or coverage level, the subcarrier spacing configuration,and/or whether to support multi-tone transmission or not, and thecoverage class (CC) or coverage level introduced to support a widecoverage service may be additionally subdivided such that the machinecommunication terminal or the machine communication device may transmitdata using optimal configuration. Further, the number of repetition maybe increased, when the coverage class (CC) or coverage level is changed,by minimizing the change in coverage class (CC) or coverage level, andan operation time of the terminal, due to standing by up to PRACHresource corresponding to the coverage level, may be reduced to reduceenergy consumption and to enhance delay time performance.

By the random access method for the uplink data transmission by themachine communication terminal or the machine communication device whichoperates in the cellular based IoT system according to exampleembodiments of the present invention, the machine communication terminalor the machine communication device can maximize utilization of thetransmission methods which are subdivided depending upon the subcarrierspacing and/or multi-tone configuration within the coverage class orcoverage level, and as a result, the increases in the operation time andthe delay time at the machine communication terminal or the machinecommunication device can be alleviated by minimizing the change incoverage class or coverage level, thereby enhancing the performance ofthe energy consumption and the delay time.

Random access for uplink data retransmission can be simplified byefficiently using the subcarrier spacing and/or multi-tone transmissionconfiguration of the machine communication terminal or the machinecommunication device to reduce the delay time and the energy consumptionat the machine communication terminal or the machine communicationdevice.

Further, example embodiments of the present invention may provide atransmission protocol which can enhance the operation of the terminalperforming small data transmission in an IoT environment. The delay timeand energy consumption at terminals that transmit small data in thecellular based IoT system can be reduced through small data transmittingmethods provided by example embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating a PRACH resource configurationin a time-frequency domain in the existing LTE environment.

FIG. 2 is a conceptual view for describing uplink single-tonetransmission when 3.75 kHz subcarrier spacing is used in Narrowband-Internet of Things (NB-IoT).

FIG. 3 is a conceptual view for describing uplink single-tonetransmission or multi-tone transmission when the 15 kHz subcarrierspacing is used in the Narrow band-Internet of Things (NB-IoT).

FIG. 4 is a conceptual view illustrating a PRACH resource configurationincluding a single-tone preamble and a multi-tone preamble.

FIG. 5 is a flowchart for describing a random access process between amachine communication terminal and a base station in cellular basednarrowband machine communication according to an example embodiment ofthe present invention.

FIG. 6 is a flowchart for describing a Message 3 collision by selectionthe same preamble by a terminal during a random access operation.

FIG. 7 is a flowchart for describing an operation when Message 3 is notyet transmitted in FIG. 6 .

FIG. 8 is a conceptual view illustrating the situation of using PRACHresources and the order of using PRACH resources depending on a basestation environment and a coverage level according to an exampleembodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a PRACH preamble resourceconfiguration for each coverage level of FIG. 8 .

FIG. 10 is a flowchart illustrating a random access method for uplinkdata transmission considering a coverage level.

FIG. 11 is a flowchart illustrating a random access method for uplinkdata transmission of a terminal considering a coverage level and asubcarrier spacing and/or multi-tone configuration according to anexample embodiment of the present invention.

FIG. 12 is a flowchart illustrating a random access method for uplinkdata transmission of a terminal considering a coverage level and asubcarrier spacing and/or multi-tone configuration according to anotherexample embodiment of the present invention.

FIG. 13 is a flowchart illustrating an example of resource allocationfor performing a random access for the uplink data transmission of theterminal considering the coverage level and a subcarrier spacingconfiguration according to another example embodiment of the presentinvention.

FIG. 14 is a flowchart illustrating an example of resource allocationfor performing a random access for uplink data transmission of aterminal considering a coverage level and a subcarrier spacingconfiguration according to yet another example embodiment of the presentinvention.

FIG. 15 is a schematic block diagram of an NB-IoT terminal according toan example embodiment of the present invention.

FIG. 16 is a schematic block diagram of an NB-IoT communication systemaccording to an example embodiment of the present invention.

FIG. 17 is a flowchart of a message exchange procedure with a basestation, which is used for describing a transmission request and atransmission process of small data of an NB-IoT terminal according to anexample embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention may have various modifications and variousembodiments and specific embodiments will be illustrated in the drawingsand described in detail.

However, this does not limit the present invention to specificembodiments, and it should be understood that the present inventioncovers all the modifications, equivalents and replacements includedwithin the idea and technical scope of the present invention.

Terms such as first, second, and the like may be used to describevarious components and the components should not be limited by theterms. The terms are used only to discriminate one constituent elementfrom another component. For example, a first component may be referredto as a second component, and similarly, the second component may bereferred to as the first component without departing from the scope ofthe present invention. A term ‘and/or’ includes a combination of aplurality of associated disclosed items or any item of the plurality ofassociated disclosed items.

It should be understood that, when it is described that a component is“connected to” or “accesses” another component, the component may bedirectly connected to or access the other component or a third componentmay be present therebetween. In contrast, it should be understood that,when it is described that an element is “directly connected to” or“directly access” another element, it is understood that no element ispresent between the element and another element.

Terms used in the present application are used only to describe specificembodiments, and are not intended to limit the present invention. Asingular form may include a plural form if there is no clearly oppositemeaning in the context. In the present application, it should beunderstood that term “include” or “have” indicates that a feature, anumber, a step, an operation, a component, a part or the combinationthereof described in the specification is present, but does not excludea possibility of presence or addition of one or more other features,numbers, steps, operations, components, parts or combinations thereof,in advance.

If it is not contrarily defined, all terms used herein includingtechnological or scientific terms have the same meanings as thosegenerally understood by a person with ordinary skill in the art. Termswhich are defined in a generally used dictionary should be interpretedto have the same meaning as the meaning in the context of the relatedart, and are not interpreted as an ideal meaning or excessively formalmeanings unless clearly defined in the present application.

A terminal may be referred to as a mobile station (MS), user equipment(UE), a user terminal (UT), a wireless terminal, an access terminal(AT), a fixed or mobile subscriber unit, a subscriber station (SS), acellular phone, a wireless device, a wireless communication device, awireless transmit/receive unit (WTRU), a mobile node, a mobile, a mobilestation, a personal digital assistant (PDA), a smart phone, a laptop, anetbook, a personal computer, a wireless sensor, a consumer electronicdevice (CE), or other terms.

Various embodiments of the terminal may include the cellular phone, thesmart phone having a wireless communication function, the personaldigital assistant (PDA) having the wireless communication function, awireless modem a portable computer having the wireless communicationfunction, a photographing device such as a digital camera having thewireless communication function, a wearable device having the wirelesscommunication function, a gaming device having the wirelesscommunication function, music storing and playing home appliances havingthe wireless communication function, Internet home appliances capable ofwireless Internet access and browsing, and portable units or terminalsintegrating combinations of the functions, but are not limited thereto.The base station generally represents a fixed point which communicateswith the terminal and may generally include a base station, Node-B,eNode-B, an advanced base station (ABS), an HR-BS, a site controller, abase transceiver system (BTS), an access point (AP), or predeterminedother type interfacing devices which may operate in a wirelessenvironment, but is not limited thereto.

The base station may be a part of a RAN which may include other basestations and/or network elements (not illustrated) such as a basestation controller (BSC), a radio network controller (RNC), relay nodes,and the like. The base station may be configured to transmit and/orreceive radio signals in a specific geographical area which may bereferred to as a cell (not illustrated).

The cell may also be partitioned into cell sectors. For example, thecell associated with the base station may be partitioned into 3 sectors.Therefore, in an example embodiment, the base station may include threetransceivers, that is, one transceiver for each sector of the cell. Inanother example embodiment, the base station may use multiple-inputmultiple output (MIMO) technology, and as a result, the base station mayuse multiple transceivers for each sector of the cell.

Hereinafter, the terminal includes a machine communication terminal forimplementing machine communication with a sensor and a communicationfunction therein. For example, the machine communication terminal mayinclude a machine type communication (MTC) terminal or a Narrow bandInternet of Things (NB-IoT) terminal.

The Narrow band Internet of Things (NB-IoT) terminal represents aterminal capable of accessing a radio access network of a channelbandwidth with 180 kHz of NB-IoT which is a cellular based narrow bandtechnology for implementing a low-power IoT network providing extendedcoverage in a licensed band. The corresponding narrow band width mayoperate in an in-band mode allocating and using some of resources in theexisting LTE network, a guard-band mode using a protection frequencyband, and a stand-alone mode using a portion within a GSM band.

Hereinafter, preferred example embodiments of the present invention willbe described in detail with reference to the accompanying drawings. Indescribing the present invention, like reference numerals refer to likeelements in the drawings for easy overall understanding and a duplicateddescription of like elements will be omitted.

In the case of the NB-IoT, 1 PRB is divided into 12 subcarriers in orderto support an IoT service in a 200-kHz band of the existing GSM, and 1PRB may be stretched by 6 times in a time domain (6:1 time stretch)instead of reducing the existing bandwidth by approximately 1/6 ratio.The NB-IoT may have a plurality of coverage levels or coverage classesand the coverage level or coverage class may be classified into threetypes of normal coverage (144 dB MCL), robust coverage (154 dB MCL), andextreme coverage (164 dB MCL).

NB-PRACH uplink transmission may be performed by frequency hoppingtogether with single-tone transmission which may guarantee performanceand provide low power and low complexity in an extreme coverageenvironment.

NB-PRACH uses 3.75 kHz subcarrier spacing for the single-tonetransmission, and 3.75 kHz subcarrier spacing can provide more preamblesand more enhanced performance in the extreme coverage environment than15 kHz such that 3.75 kHz subcarrier spacing may support a maximum cellsize of 40 km.

Further, in the NB-PRACH, the length of two cyclic prefixes (CPs) may beprovided in order to support different cell sizes.

NB-PRACH repetition transmission is a method that configures NB-PRACHresources for supporting NB-IoT terminals which belong to differentcoverage classes. The terminals may operate by selecting the NB-PRACHhaving appropriate repetition transmission according to the coverageclass.

The NB-PRACH repetition transmission may be provided at a predeterminednumber in a predetermined set (1, 2, 4, 8, 16, 32, 64, and 128) and theeNB may be configured to perform a maximum of three types of NB-PRACHrepetition transmission from the predetermined set by considering threecoverage classes.

With regard to power ramping of the NB-PRACH, when one or morerepetition levels are configured in a cell, the terminal transmits theNB-PRACH with the maximum power except for a lowest repetition levelhaving a highest coverage class, and in other cases, the terminaltransmits the NB-PRACH by using the power ramping to implement alow-power operation.

The NB-IoT terminal may fail to receiving Msg4 after RAR is received andMsg3 is transmitted during the random access process. In this case, theterminal repeatedly retransmits the Msg3 and when the terminal fails toconsecutively receiving the Msg4 at a predetermined number of times, theterminal determines that the coverage classes does not coincide witheach other and changes the coverage class. The number of retransmissionuntil the coverage class is changed may be indicated in downlink controlinformation (DCI) in an NB-PDCCH.

Hereinafter, an NPRACH may be used as the same as the NB-PRACH.

In the NB-IoT, the 3.75 kHz and 15 kHz subcarrier spacings may be usedduring the uplink (UL) transmission.

With regard to a UL grant, uplink (UL) subcarrier spacing may have 3.75kHz or 15 kHz, and 3.75 kHz or 15 kHz may be indicated as 1 bitinformation to be included in the UL grant of the RAR message. That is,in the NB-IoT, whether which subcarrier spacing among 3.75 kHz or 15 kHzis used may be indicated by using 1 bit in the UL grant (uplink grant)of the RAR message transmitted by the base station.

In the NB-IoT, two subcarrier spacings such as 3.75 kHz and 15 kHz maybe used in detail during the random access process via the RAR message.

With regard to NB-PRACH subcarrier locations, a frequency location in asubcarrier offset may have 7 values, for example, 0, 12, 24, 36, 2, 18,and 34 and may be represented by 3 bits.

The number of subcarriers may have 4 values, for example, 12, 24, 36,and 48 and may be represented by 2 bits.

The NB-PRACH may be repeated by using contiguous subframes within oneperiod. In detail, NB-PRACH repetitions may be transmitted consecutively(transmitted back to back) within contiguous subframes within one periodfor the NB-PRACH.

With regard to the NB-PRACH subcarrier locations, the frequency locationin the subcarrier offset may vary depending on the number (for example,12, 24, 36, and 48) of subcarriers. In detail, the frequency location inthe subcarrier offset may vary such as 0, 12, 24, 36, 2, 18, and 34depending on the number (for example, 12, 24, 36, and 48) ofsubcarriers, and the number of subcarriers and the frequency location inthe subcarrier offset may be predefined in a predetermined table.

With regard to the NB-PRACH, adjustment of the uplink transmissiontiming may be applied from the start of first NB-PUSCH transmissionwhich starts at a predetermined time, for example, 12 ms, aftertransmission of a corresponding timing advance command terminates.Herein, the timing advance command may be included in the RAR to betransmitted via the RAR.

In the NB-IoT, with regard to the NB-PRACH configuration, a maximum of 3NB-PRACH resource configurations may be used in one cell.

The PRACH resources may be divisionally used for the single-tone andmulti-tone transmission. In particular, the PRACH subcarrier may bedivisionally used for the single-tone and multi-tone transmission in thePRACH configuration depending on the coverage level presented in FIG. 9.

When the terminal performs an RACH procedure in order to transmit theMsg3 through the single tone and the multi-tone, the terminal may dividethe subcarrier resources to be used in the PRACH according to thesingle-tone transmission or the multi-tone transmission. In detail, thesubcarrier for the single-tone transmission may be particularlyguaranteed (may not be 0) in a specific PRACH resource. For example, aratio of the number of subcarriers to be used for the single tone MSG3transmission may not become 0 in at least one resource in which thenumber of NB-PRACH repetition is other than 32, 64, and 128.Alternatively, the ratio of the number of subcarriers to be used for thesingle tone MSG3 transmission may not become 0 at least in resource inwhich the number of NB-PRACH repetition is 32, 64, 128.

The multi-tone MSG3 transmission may not be supported when the number ofNB-PRACH repetition is 32, 64, 128.

A range of the subcarrier resource used for the multi-tone transmissionmay be expressed by using 2 bits. For example, a starting subcarrierindex in a subcarrier range reserved for UE which supports themulti-tone Msg transmission may be expressed through, for example, 2bits ({0, 1/3, 2/3, 1}×N_sc{circumflex over ( )}NB-PRACH). Herein,N_sc{circumflex over ( )}NB-PRACH represents the total number ofsubcarriers and 1/3×N_sc{circumflex over ( )}NB-PRACH means 1/3 of thetotal subcarrier number.

Further, when there is no subcarrier resource for the multi-tone Msg3transmission, the subcarrier for the single-tone Msg3 transmission maybe used. When the UE selects the resource reserved for the single toneMSG3 message, the MSG3 message may be allocated to the single tone. Thismeans that the UE needs to use the NB-PRACH resources reserved for thesingle tone MSG3 transmission when a reserved subcarrier range, which isused by the UE that all PRACH resources support the multi-tone MSG3transmission, does not exist.

In the NB-PRACH resource, other subcarriers (subcarriers other than thesubcarrier to be used in the multi-tone transmission) may be used as arange for the single tone MSG3 transmission.

Msg3 message subcarrier allocation may be the same as UL grantallocation on the NB-PDCCH.

The Msg3 repetition number may be the same as the NB-PUSCH repetitionnumber.

From the viewpoint of a technical effect, since the 3.75 kHz subcarrierspacing is relatively excellent in power spectral density (PSD)performance, the 3.75 kHz subcarrier spacing may operate robustly evenin an environment in which the channel state is not good, the 15 kHzsubcarrier spacing may enhance uplink transmission rate of the terminalthrough a relatively wide bandwidth, but the 15 kHz subcarrier spacingneeds to be used in the good channel state. Therefore, two subcarrierspacings such as 3.75 kHz and 15 kHz may be provided to be suitable forthe channel state of the terminal, thereby leading to performanceenhancement. The multi-tone transmission may enhance the transmissionrate as compared with the single-tone transmission by using multiplesubcarriers.

An equation given below, which is used in RANI may be reused for thepower ramping in the NB-PRACH. However, a term (−10*log10(numRepetitionPerPreambleAttempt) is added and a repetitiontransmission effect may be compensated through the added term.

-   -   REAMBLE_RECEIVED_TARGET_POWER is defined as        preambleInitialReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_TRANSMISSION_COUNTER−1)*powerRampingStep−10*log        10(numRepetitionPerPreambleAttempt), and in this case,        DELTA_PREAMBLE is 0.

In case of colliding transmissions, with respect to a standaloneoperation and a guard band operation, NB-IoT channels and signals otherthan an NB-PBCH may occupy resource elements (REs) corresponding to LTEcell-specific reference signals (CRS) calculated according to physicalCell_ID. NB-IoT signaling of LTE channel state information-referencesignals (CSI-RS) or positioning reference signals (PRS) does not exist.The NB-PDCCH and the NB-PDSCH may be rate-matched to the periphery ofthe LTE cell-specific reference signals (CRS) for an in-band operation.

With regard to a scheduling collision, the NB-IoT UE that receives thegrant from the NB-PDCCH need not additionally monitor the NB-PDCCH for apredetermined DL grant or UL grant during a time period between thestart of the corresponding NB-PDSCH or NB-PUSCH transmission and the endof the NB-PDCCH scheduling the grant.

With regard to PRACH collision handling for the NB-IoT, UEs in lowercoverage may treat NB-PRACH opportunities collision with higher coveragelevel(s) as invalid. The UEs may use only NB-PRACH opportunities validfor Msg1 transmission.

In long term evolution (LTE), the terminal may start the random accessprocess when a link configuration or reconfiguration with the basestation eNodeB (eNB) for data transmission. The random access mayoperate according to a non-contention scheme or a contention schemeaccording to the purpose.

The non-contention scheme random access process is used only for aspecial purpose such as handover and in a normal case, the terminalconfigures a connection with the eNB through the contention schemerandom access to transmit data.

FIG. 1 is a conceptual view illustrating a PRACH resource configurationin a time-frequency domain in the existing LTE environment.

Referring to FIG. 1 , a resource that performs a random access includesa continuous time-frequency random access resource 12 called a randomaccess (RA) slot and the terminal transmits a preamble in an RA slot tostart a transmission request.

The resource in which the preamble is transmitted is referred to as aphysical random access channel (PRACH) and is used while being allocatedto a predetermined part of a physical uplink shared channel (PUSCH). Asillustrated in FIG. 1 , in a frequency domain, a PRACH resource has abandwidth corresponding to 6 resource blocks (RBs).

Each cell provides 64 preambles and some of the preambles are reservedto support the non-contention scheme random access and the residualpreamble resources are classified into resources of Group A and Group B.Group A is used for transmitting a small packet and Group B is used fortransmitting a large packet. Besides, random access related parametersincluding periodicity of the RA slot, the number of preambles used inthe contention based random access, a message size maximally permittedin Group A, and the like are transferred to the terminal through asystem information block 2 (SIB 2) message.

A reduced 180-kHz band may be allocated and used in the case of uplinkand random access transmission of Narrow Band-Internet of Thing (NB-IoT)and the NB-IoT uplink and random access transmission may be divided intosingle-tone transmission using a single subcarrier and multi-tonetransmission using multiple subcarriers.

FIG. 2 is a conceptual view for describing uplink single-tonetransmission when 3.75 kHz subcarrier spacing is used in Narrowband-Internet of Things (NB-IoT) and FIG. 3 is a conceptual view fordescribing uplink single-tone transmission or multi-tone transmissionwhen the 15 kHz subcarrier spacing is used in the Narrow band-Internetof Things (NB-IoT).

In the case of the single-tone transmission, single-tone transmission 20using the 3.75 kHz subcarrier spacing as illustrated in FIG. 2 orsingle-tone transmission 30 using the 15 kHz subcarrier spacing asillustrated in FIG. 3 is available. In the case of the single-tonetransmission, the data rate is low by using a small frequency band, butpower concentrates on the frequency band, and as a result, coverageefficiency is high even in the environment in which the channel state isnot good and device cost and device complexity may be reduced ascompared with the multi-tone transmission scheme.

In the case of the multi-tone transmission, the terminal may performmulti-tone transmission 35 using the 15 kHz subcarrier spacingillustrated as illustrated in FIG. 3 . In the case of the multi-tonetransmission, the high data rate is guaranteed by using multiplesubcarriers, but a comparatively wide bandwidth is used, and as aresult, the multi-tone transmission needs to be under the environment inwhich the channel state is good and the device cost may increase and thedevice complexity may increase due to the increased signal processing.

FIG. 4 is a conceptual view illustrating a PRACH resource configurationincluding preambles for single-tone and multi-tone Msg3 transmission inthe NB-IoT system.

Referring to FIG. 4 , the PRACH resource may be constituted by asingle-tone preamble 40 numbered with 0, 1, . . . , (N_(sc)^(NPRACH)N_(MSG3) ^(NPRACH)) and a multi-tone preamble 50 numbered with(N_(sc) ^(NPRACH) N_(MSG3) ^(NPRACH)), . . . , (N_(sc) ^(NPRACH)−1).

Besides, the PRACH resource may be defined as the following parameterstransmitted from the base station the terminal.

N_(period) ^(NPRACH): NPRACH resource periodicity)

N_(scoffset) ^(NPRACH): Frequency location of the first sub-carrierallocated to NPRACH

N_(sc) ^(NPRACH): The number of sub-carriers allocated to NPRACH)

N_(rep) ^(NPRACH): The number of NPRACH repetition per attempt

N_(start) ^(NPRACH): NPRACH starting time

N_(MSG3) ^(NPRACH): Fraction for calculating starting subcarrier indexfor the range of NPRACH subcarriers reserved for indication of UEsupport for multi-tone msg3 transmission

Hereinafter, the contention based random access process will bedescribed with reference to FIGS. 5 and 6 .

FIG. 5 is a flowchart for describing a random access process between amachine communication terminal and a base station in cellular basednarrowband machine communication according to an example embodiment ofthe present invention and FIG. 6 is a flowchart for describing a Message3 collision by selection the same preamble by a terminal during a randomaccess operation.

1. Message 1 Transmission [Preamble Transmission]

Referring to FIG. 5 , the NB-IoT terminal starts the random access andtransmits the preamble to the station (step 501). In this case, theterminal randomly selects one preamble in the resource corresponding tothe coverage level and transmits the selected preamble to the basestation. Different preambles transmitted to the base station may bereceived by the base station by orthogonality between the preambles.

As another case, referring to FIG. 6 , even when two or more terminalsUE 1 550 and UE 2 560 simultaneously transmit the same preamble, thesame preambles are the same signal, and as a result, the base stationmay receive the preamble (steps 601 and 603). However, when two or moreterminals select the same preamble, the collision may occur during thesubsequent Message 3 transmission process of the terminal.

2. Message 2 Transmission [Random Access Response Transmission]

The base station transmits the random access response (RAR) messageincluding resource information for timing alignment (TA) andtransmission of the Message3 to the terminal through a physical downlinkshared channel (PDSCH) in response to a preamble request which wassuccessfully received by the base station. The resource information fortiming alignment (TA) and transmission of the Message3 may be, forexample, a physical uplink shared channel (PUSCH) resource. The terminalmay determine whether the preamble, which the terminal previouslyreceives, is successfully received or not by receiving the RAR message.When it is determined that the terminal unsuccessfully transmits thepreamble, the terminal transmits the preamble in order to reperform therandom access process in a new RA slot after a random backoff time. Whenthe transmission failure of the preamble occurs more than apredetermined number of times, the terminal informs a problem in therandom access process to a higher layer.

3. Message 3 [Connection Request Transmission]

The terminal transmits the Message3, which represents a connectionrequest, via a reserved resource in the physical uplink shared channel(PUSCH) after receiving the random access response (RAR) (505). TheMessage 3 is transmitted by an HARQ scheme. As described in the Message1 transmitting step, referring to FIG. 6 , when a plurality of terminalstransmits the same preamble (steps 601 and 603) and the base stationthus transmits the random access response (RAR) (steps 605 and 607), theplurality of terminals transmits the Message 3 via the same PUSCHresource (steps 611 and 613), and as a result, the collision occurs.

Herein, the Message 3 (Msg3) is a message by which the terminal performthe connection request to the base station for uplink data transmission.The terminal may perform uplink transmission in the allocated resourcewhen receiving a Contention Resolution, which is a response from thebase station, after transmitting the Message 3.

When the terminal initially transmits the preamble, it is determinedthat the Msg3 is not yet transmitted, the terminal selects and transmitsthe preamble in the PRACH resource corresponding to the coverage leveldetermined by the terminal. Alternatively, when the terminal transmitsthe preamble second time or more due to a failure in transmission of theMsg3, it is determined that the Msg3 is under retransmission, and theterminal attempts the random access by randomly selecting the preambleagain in a resource in which a first preamble is selected. When thenumber of preamble transmission is more than the maximum number ofpreamble transmission, the coverage level is changed and the number ofpreamble transmission is again initialized to 1.

4. Message 4 [Contention Resolution Transmission]

The base station that receives the Message 3 from the terminal respondsto the terminal using the contention resolution (CR) included in thephysical uplink shared channel (PDSCH) and approves the connectionrequest to the terminal (step 507). In FIG. 6 , the Message 3 collisionof two terminals occurs (step 611 or 613). In this case, the terminalmay not receive the contention resolution (CR) from the base station andtransmits a new preamble in the new RA slot after the random backofftime. When the transmission failure of the preamble occurs more than aspecific number of times, the terminal determines that it is impossibleto use a network.

FIG. 7 is a flowchart for describing a random access operation whenMessage 3 is not yet transmitted in FIG. 6 .

Referring to FIG. 7 , the machine communication terminal determineswhether the Message 3 (Msg3) is not yet transmitted during the randomaccess process (step 710). In this case, a state in which the Msg3 isnot yet transmitted represents a case where the first preamble istransmitted.

As the determination result, when the Message 3 (Msg3) is not yettransmitted, the PRACH resource is selected by considering the coveragelevel and whether to support the multi-tone transmission or not (step720). Alternatively, as the determination result, when the Message 3(Msg3) is not yet transmitted, the PRACH resource may be selected byconsidering the coverage level, the subcarrier spacing and/or whether tosupport the multi-tone transmission or not. In detail, the case wherethe Message 3 (Msg3) is not yet transmitted represents a case where therandom access process is initialized and the first preamble istransmitted, and the PRACH resource may be selected by considering thecoverage level and whether to support the multi-tone Message 3 (Msg3)transmission or not. In detail, the case where the Message 3 (Msg3) isnot yet transmitted represents a case where the number of preambletransmission is initialized due to exceeding the maximum number ofpreamble transmission and thereafter, the first preamble is transmittedunder other conditions by the machine communication terminal, or a casewhere first random access preamble transmission is performed withoutexceeding the maximum number of preamble transmission.

FIG. 8 is a conceptual view illustrating a PRACH resource use situationdepending on a base station environment and a coverage level accordingto an example embodiment of the present invention.

The present invention provides a random access performing methodconsidering the coverage level (CL) and the subcarrier spacing and/orthe multi-tone configuration in the cellular based IoT system, forexample, the NB-IoT system.

Referring to FIG. 8 , in the example embodiment of the presentinvention, a base station 880 provides three coverage levels (CLs), and,for each coverage level (CL), configures the resources so as to use thePRACH resources by dividing the PRACH resources according to thesubcarrier spacing and/or multi-tone configuration. However, this isjust one of example embodiments of the resource configuration in thepresent invention according to the performance characteristic of thesubcarrier spacing and/or multi-tone configuration and a specificconfiguration combination may be excluded or added. An exampleembodiments of the present invention will be described in a direction tomaximally use sequential performance according to the subcarrier spacingand/or multi-tone configuration.

Referring to FIG. 8 and Table 1, the terminal may use three subcarriercombination configurations of 1) 15 kHz, multi-tone, 2) 15 kHz,single-tone, and 3) 3.75 kHz, single-tone according to the channelstate, for example, channel state at a cell center, a good channelstate, and an extreme coverage state.

-   -   Further, in response thereto, the base station may divide even        the preamble resources according to a set value which is        specifically supported according to each coverage level. In this        case, the range of the preamble resource may be determined        according to α, β, and the like and the corresponding        information is included in a message representing information        constituting the PRACH resource to be transferred from the base        station to the terminal similarly to the related art. It is        assumed that since CL1 has a best channel state, the CL1 uses        all of three subcarrier and/or multi-tone configurations, since        CC2 has a relatively better channel state, the CC2 uses two        subcarrier and/or multi-tone configuration of 2) 15 kHz,        single-tone and 3) 3.75 kHz, single tone, and since CC3 has an        extreme channel state, the CC3 uses only one subcarrier and/or        multi-tone configuration of 3.75 kHz, single tone.

In the example embodiment of FIG. 8 , the preamble resources of the CL1are partitioned by using a ratio value of α₁ and β₁ in order topartition the respective preamble resources of the CL1 into the (15 kHz,multi-tone), (15 kHz, single-tone), and (3.75 kHz, single-tone)resources and a ratio value of α₂ is used in order to partition therespective preamble resources of the CL2 into the (15 kHz, single-tone)and (3.75 kHz, single-tone) resources.

The terminal performs synchronization with the base station for theuplink data transmission and receives system information from the basestation while being synchronized with the base station and during thisprocess, the terminal determines the CL and the subcarrier spacingand/or multi-tone configuration according to the channel state.Thereafter, the terminal receives PRACH resource information from thebase station in order to perform the random access at the correspondingCL. During the random access process, the terminal selects the preambleby considering the selected CL and subcarrier spacing and/or multi-toneconfiguration and transmits the selected preamble to the base station.Thereafter, the terminal receives the resource information which may beused for transmitting the Msg3 to request the connection for the uplinktransmission by receiving the random access response (RAR) from the basestation. When the terminal may not receive the RAR, the terminaltransmits the preamble again and selects and transmits the preamble inthe same PRACH resource as the first selected configuration. When thenumber of retransmission is more than the maximum number of preambleretransmission times, the terminal changes the coverage level andthereafter, selects and transmits the preamble in the PRACH resourcecorresponding to the subcarrier spacing and/or multi-tone configurationavailable at the corresponding coverage level.

The terminal transmits the Msg3 in the allocated resource by the HARQscheme and when the terminal fails to the HARQ transmission due to thechange in channel state or when the terminal may not receive Msg4 evenafter transmitting the Msg3, the terminal transmits the preamble againand selects and transmits the preamble in the same PRACH resource as thefirst selected configuration. When the number of retransmission is morethan the maximum number of preamble retransmission, the terminal changesthe coverage level and the subcarrier spacing and/or multi-toneconfiguration and thereafter, selects and transmits the preamble in thecorresponding PRACH resource.

In respect to all cases, when there is no subcarrier spacing and/ormulti-tone configuration selectable with respect to the correspondingCL, the terminal selects the CL that supports a channel state lower byone step than current channel state, and thereafter, selects thesubcarrier and/or multi-tone configuration corresponding thereto andselects the preamble resource to be transmitted in the correspondingPRACH resource.

FIG. 10 is a flowchart illustrating a random access method by a terminalfor uplink data transmission considering a coverage level in the relatedart and FIG. 11 is a flowchart illustrating a random access method foruplink data transmission of a terminal considering a coverage level anda subcarrier spacing and/or multi-tone configuration according to anexample embodiment of the present invention.

Referring to FIG. 10 , in the random access method considering thecoverage level in the related art, the terminal selects the coveragelevel and thereafter, selects and transmits the corresponding preambleresource. Thereafter, when the terminal receives the RAR from the basestation and transmits the Msg3 by the HARQ scheme, the terminal receivesthe Contention Resolution which is the response from the base station tocomplete the random access process. In this case, when the RAR is notreceived by the terminal or fail of the Msg3 HARQ transmission occurs orthe Contention Resolution is not received by the terminal, the terminalreattempts the random access by performing the preamble transmissionprocess in the same PRACH resource again. When the number of preambletransmission is more than the maximum number of preamble transmissiondetermined from the base station during this process, the terminaldetermines that the selected coverage level is not appropriate to acurrent channel state, and changes the selected coverage level to thecoverage level having a channel state lower by one step than the currentchannel state, and selects the preamble in the corresponding PRACHresource again to perform the random access procedure.

However, the procedure for reperforming the random access after changingthe coverage level (CL) has a problem that an operation time and andelay time significantly increase because the terminal needs to performa process for waiting for the physical RACH (PRACH) for performing therandom access at the changed coverage level (CL) and the random accessprocess in the corresponding PRACH again from the beginning.

Hereinafter, the random access method by the terminal considering thecoverage level and the subcarrier spacing and/or multi-toneconfiguration according to the example embodiment of the presentinvention will be described.

In the case of the non-contention based random access process, therandom access preamble is explicitly signaled from the base station (therandom access preamble to be used is explicitly expressed).

In the case of the contention based random access process, the randomaccess preamble is not explicitly signaled from the base station (therandom access preamble to be used is not explicitly expressed).

Herein, the random access processes of FIGS. 11 and 12 may be performedwhen the random access preamble to be used is not explicitly signaledfrom the base station.

Referring to FIG. 11 , by the random access method, performed by theterminal, for the uplink data transmission according to the exampleembodiment of the present invention, the terminal receives the randomaccess response (RAR) from the base station during the RACH process toreceive usable uplink resource information (step 1101).

In the allocated uplink resource, the terminal transmits the message(Mesg3) to request the connection for the uplink data transmission (step1103) and the terminal checks whether the Msg3 is unsuccessfullytransmitted or the Msg3 transmission fails due to the change in channelstate, and the like (step 1105). When the Msg is not unsuccessfullytransmitted or the Msg3 transmission does not fails, it is checked thatthe uplink transmission is successful (step 1107).

When the Msg3 is unsuccessfully transmitted or the Msg3 transmissionfails, the terminal determines whether the number of unsuccessful Msg3transmission or the number of failed Msg3 transmission is less than themaximum number of retransmission (step 1109). Herein, the maximum numberof retransmission may be included in the downlink control information(DCI).

When the number of unsuccessful Msg3 transmission or the number offailed Msg3 transmission is less than the maximum number ofretransmission times, the process returns to step 1101 and performs theRACH procedure again to receive usable uplink resource information fromthe base station and attempt transmission of the Msg3 again.

When the number of unsuccessful Msg3 transmission or the number offailed Msg3 transmission is not less than the maximum number ofretransmission times, the terminal attempts the data (Msg3) transmissionprocess by performing the RACH process again by changing the subcarrierspacing and/or multi-tone configuration to the subcarrier spacing and/ormulti-tone configuration having a transmission rate, which is lower byone step than the current transmission rate, at the same coverage level(CL) according to the example embodiment of the present inventioninstead of the operation of changing the existing coverage level (CL).In this case, the terminal may attempt transmitting the Msg3 byimmediately performing retransmission by using PRACH resourceinformation which the base station preliminarily allocates to the randomaccess response (RAR) by considering the change of the subcarrierspacing and/or multi-tone configuration according to the exampleembodiment of the present invention (Option 2) or performing the RACHprocess in the PRACH resource (alternatively, preamble resource) usingthe subcarrier spacing and/or multi-tone having a transmission rate,which is lower by one stage than the current transmission rate, withinthe same coverage level (CL) again (Option 1). When the terminalconsecutively fails to the transmission even in the current subcarrierspacing and/or multi-tone configuration, the terminal receives the PRACHresource information corresponding to the corresponding coverage level(CL) by changing the coverage level to another coverage level andthereafter, performs the RACH process.

Hereinafter, by using a detailed example, the random access method bythe terminal for the uplink data transmission according to the exampleembodiments of the present invention will be described.

When it is assumed that a specific terminal that performs the randomaccess according to the example embodiment of the present invention ispositioned at a CL2 area, the terminal selects and transmits thepreamble resource by a 15 kHz single-tone configuration of initial CL2and receive the random access response (RAR) which is the response tothe preamble transmission from the base station.

The RAR which is the response to the preamble transmission from the basestation is not received, and as a result, the preamble transmission maybe attempted again and when the RAR is not consecutively received andthe number of preamble transmission is thus more than the maximum numberof preamble transmission, the terminal immediately selects the 3.75 kHz,single-tone configuration having the maximum transmission rate of theCL3 that supports a channel state lower by one stage than the currentchannel state, and thereafter, selects the preamble in the correspondingPRACH resource to perform the random access process again.

When the number of consecutive transmission failure of the Msg3 is morethan the maximum number of retransmission during the random accessprocess, the terminal thereafter attempts the Msg3 transmission processby performing the RACH process again by selecting the 3.75 kHzsingle-tone which is the subcarrier spacing and/or multi-toneconfiguration having a transmission rate, which is lower by one stepthan the current transmission rate, at the same coverage level (CL)according to the example embodiment of the present invention instead ofthe operation of changing the existing coverage level (CL). In thiscase, the terminal may attempt transmitting the data (Msg3) byimmediately performing retransmission by using PRACH resourceinformation which the base station preliminarily allocates to the randomaccess response (RAR) by considering the change of the subcarrierspacing and/or multi-tone configuration according to the exampleembodiment of the present invention during the previous RACH process(Option 2) or performing the RACH process in the PRACH resource for the3.75 kHz single-tone of the CL2 again (Option 1). When the number ofconsecutive transmission failure of the Msg3 is more than the maximumnumber of retransmission during the random access process even in the3.75 kHz single-tone configuration, the terminal changes the coveragelevel to the CL3 and receives the PRACH resource informationcorresponding to the corresponding coverage level (CL) and thereafter,performs the RACH process.

FIG. 12 is a flowchart illustrating a random access method for uplinkdata transmission of a terminal considering a coverage level and asubcarrier spacing and/or multi-tone configuration according to anotherexample embodiment of the present invention.

Referring to FIG. 12 , by the random access method for uplink datatransmission according to another example embodiment of the presentinvention, the terminal selects the coverage level for the random accessprocess (step 1201) and selects and transmits the preamble resourcecorresponding thereto (step 1203). Thereafter, the terminal acquires theuplink resource for transmitting the Msg3 together with the RAR which isthe response from the base station. The terminal may transmit the Msg3by the HARQ scheme and when the terminal receives the Msg3 from the basestation, the terminal may finally complete the random access process byreceiving the contention resolution message from the base station.

The failure in random access process may occur because the terminal doesnot receive the RAR or unsuccessfully transmits the Msg3 orunsuccessfully receives the contention resolution. In respective cases,the terminal attempts transmitting the preamble again in order toreperform the random access process.

In the case where the terminal does not receive the RAR, that is, in thecase where the terminal unsuccessfully transmits the preamble, theterminal reperforms the random access and determines whether the numberof preamble transmission is more than the maximum number of preambletransmission (step 12130) and when the number of preamble transmissionis more than the maximum number of preamble transmission times, theterminal immediately changes the coverage level to the coverage level tosupport a channel state lower by one step than the current channel state(step 1201). The reason is that since the random access preambletransmission is performed by using the 3.75 kHz single-toneconfiguration, the terminal is incapable of performing the random accesspreamble even with the lowest configuration at the correspondingcoverage level.

The terminal attempts transmitting the Msg3 by the HARQ scheme (step1207) and determines whether the Msg3 is successful transmitted by theHARQ scheme (step 1209) and when the Msg3 is successful transmitted bythe HARQ scheme, the terminal determines whether the contentionresolution is received (step 12110).

In the case where the terminal unsuccessfully transmits the Msg3(unsuccessfully transmits the Msg3 by the HARQ scheme) or in the casewhere the terminal unsuccessfully receives the contention resolution,when it is determined that the number of preamble transmission is morethan the maximum number of preamble transmission while the terminalreperforms the random access, the terminal may reperform the randomaccess process through the method using the subcarrier spacing and/ormulti-tone configuration according to the example embodiments of thepresent invention (steps 1217, 1219, 1203, and 1201). In detail, theterminal determines whether there is a subcarrier spacing and/ormulti-tone configuration having a transmission rate lower by one stepthan the current transmission rate, which may be changed at the currentcoverage level (step 1217) and when there is the subcarrier spacingand/or multi-tone configuration, the terminal changes the subcarrierspacing and/or multi-tone configuration to the subcarrier spacing and/ormulti-tone configuration having a transmission rate lower by one stepthan the current transmission rate, which may be changed at the currentcoverage level (step 1219) and thereafter, selects and transmits thepreamble in the corresponding PRACH resource (step 1203) to reperformthe random access process. In this case, the terminal may start therandom access process the preamble transmission again according to theexample embodiments of the present invention (Option 1) or immediatelytransmit the Msg3 by the HARQ scheme by using the uplink resourceinformation which the base station preliminarily allocates to the RAR byconsidering the subcarrier spacing and/or multi-tone configurationchange of the present invention while performing the previous randomaccess (Option 2). When the terminal consecutively unsuccessfullytransmits the Msg3 or unsuccessfully receives the contention resolution,the terminal performs the random access in the PRACH resourcecorresponding to the corresponding coverage level by changing thecurrent coverage level to the lower coverage level by one step.

Hereinafter, by using a detailed example, the random access method bythe terminal for the uplink data transmission according to anotherexample embodiment of the present invention will be described.

When it is assumed that a specific terminal that performs the randomaccess process of the uplink data transmission according to the exampleembodiment of the present invention is positioned at a CL2 area, theterminal selects and transmits the preamble resource by a 15 kHzsingle-tone configuration of initial CL2. The RAR which is the responseto the preamble transmission from the base station is not received, andas a result, the preamble transmission may be attempted again and whenthe RAR is not consecutively received and the number of preambletransmission is thus more than the maximum number of preambletransmission, the terminal immediately selects the 3.75 kHz, single-toneconfiguration having the maximum transmission rate of the CL3 thatsupports a channel state lower by one stage than the current channelstate, and thereafter, selects the preamble in the corresponding PRACHresource to perform the random access process again.

When the terminal consecutively unsuccessfully transmits the Msg3 afterreceiving the random access response (RAR) or unsuccessfully receivesthe contention resolution, the terminal may perform the random access byselecting the preamble in the same PRACH resource as the first selectedconfiguration. When the number of transmission is more than the maximumnumber of transmission, the terminal performs the random access processagain by selecting the preamble in the corresponding PRACH resource byselecting the 3.75 kHz single-tone which is the subcarrier spacingand/or multi-tone configuration having the lower transmission rate byone step within the same coverage level (CL or CL2) according to theexample embodiment of the present invention instead of the operation ofchanging the existing coverage level (CL). In this case, the terminalmay immediately transmit the Msg3 by using the uplink resourceinformation which the base station preliminarily allocates to the randomaccess response (RAR) by considering the change of the subcarrierspacing and/or multi-tone configuration according to the exampleembodiment of the present invention during the previous random accessprocess (Option 2) or performing the random access process in the PRACHresource for the 3.75 kHz single-tone of the CL2 again (Option 1). Whenthe terminal consecutively unsuccessfully transmits the Msg3 or does notreceive the contention resolution even in the 3.75 kHz single-toneconfiguration, the terminal changes the coverage level to the CL3 andwaits for the PRACH resource corresponding to the corresponding coveragelevel (CL) and thereafter, performs the random access process.

When it is assumed that a specific terminal for the random access methodprocess of the uplink data transmission according to another exampleembodiment of the present invention is positioned on the edge of a CL1area, the terminal selects the preamble resource by the 15 kHzsingle-tone configuration of initial CL2 and starts the random accessprocess.

In this case, when the number of transmission is more than the maximumnumber of transmission due to the unsuccessful random access executioncaused by not consecutively receiving the RAR, the terminal changes thecoverage level to the CL2 which is the coverage level supporting achannel state lower by one step than the current channel state, andthereafter, selects the 15 kHz single-tone configuration supporting thehighest transmission rate in the corresponding CL and performs therandom access with the corresponding PRACH resource (preamble resource)again.

Alternatively, when the number of transmission is more than the maximumnumber of transmission due to unsuccessful Msg3 HARQ transmission orunsuccessful contention resolution reception after receiving the RAR,the terminal may reattempt the random access again by selecting thePRACH resource (alternatively, preamble resource) using the 15 kHzsingle-tone configuration which is the subcarrier spacing and/ormulti-tone configuration having a transmission rate, which is lower byone step than the current transmission rate, within the same coveragelevel (CL) according to another example embodiment of the presentinvention instead of the operation of changing the existing coveragelevel (CL). In this case, the terminal may immediately transmit the Msg3instead of transmitting the preamble by using the PRACH resourceinformation which the base station preliminarily allocates to the randomaccess response (RAR) by considering the change of the subcarrierspacing and/or multi-tone configuration according to another exampleembodiment of the present invention during the previous random accessprocess (Option 2) or performing the random access process in the PRACHresource for the 15 kHz single-tone of the CL1 again as described above(Option 1). When the terminal consecutively unsuccessfully transmits theMsg3 or does not receive the contention resolution even in the 15 kHzsingle-tone configuration, the terminal may make the reattemption by theOption 1 or Option 2 operation again by changing the configuration tothe 3.75 kHz single-tone configuration. When the terminal unsuccessfullytransmits the Message 3 even in the 3.75 kHz single-tone configuration,the terminal determines that all configurations provided at the CL1 areunavailable in communication and may change the coverage level to theCL2 and thereafter, reperform the random access process or the Message 3transmission process by the 15 kHz single-tone configuration provided atthe corresponding CL.

That is, when the number of transmission is more than the maximum numberof transmission due to unsuccessful Msg3 transmission or unsuccessfulcontention resolution reception during the random access process, theterminal may reperform the random access by the subcarrier spacingand/or multi-tone combination provided within the current coverage leveland finally changes the current coverage level and stepwise perform therandom access process for the uplink data transmission again when theterminal unsuccessfully transmits the Msg3 or unsuccessfully receivesthe contention resolution up to the last step of the provided subcarrierspacing and/or multi-tone configuration. However, when the number oftransmission is more than the maximum number of transmission due to thefailure in random access caused by not receiving the RAR, the terminalimmediately changes the current coverage level to a channel state lowerby one step than the current channel state to perform the random accessprocess again.

Referring to FIG. 8 , according to the example embodiment of the presentinvention, an example is illustrated, in which when the terminalperforms the random access for the uplink data transmission, the PRACHresources (alternatively, preamble resources) are sequentially selectedin an arrow direction so as to achieve stepwise performance according tothe subcarrier spacing and/or multi-tone configuration after consecutivefailure in random access during the Msg3 transmission or contentionresolution reception.

According to another example embodiment of the present invention, whenit is assumed that the specific terminal performing the random access ofthe terminal for the uplink data transmission is positioned on the edgeof the CL1 area, the terminal may perform the random access processwithin the coverage level only by changing the subcarrier configuration.

That is, referring to FIG. 13 , when the terminal performs the randomaccess by selecting the 15 kHz single-tone configuration of the initialCL1 and thereafter, consecutively unsuccessfully transmits the Msg3 ordoes not receive the contention resolution, the terminal changes the 15kHz single-tone configuration of the CL1 which is the same coveragelevel to the 3.75 kHz single-tone configuration without changing thecoverage level and thereafter, attempts the random access process.Thereafter, when the random access fails by the terminal, the terminalmay change the coverage level to the CL2 and thereafter, uses the 15 kHzsingle-tone configuration and when the random access fails by theterminal again, the terminal may attempt the random access by the 3.75kHz single-tone configuration. When the random access fails by theterminal again, the terminal may change the coverage level to the CL3and thereafter, attempt the random access by the 3.75 kHz single-toneconfiguration last. In this case, in the case where the random accessfails by the terminal, the terminal performs the random access and thus,the number of preamble retransmission is more than the maximum number oftransmission due to unsuccessful Msg3 HARQ transmission or non-receptionof the contention resolution message and the case is defined to have thesame meaning even in a description to be mentioned below.

According to yet another example embodiment of the present invention,when it is assumed that the specific terminal performing the randomaccess of the terminal for the uplink data transmission is positioned onthe edge of the CL1 area, the terminal may perform the random accessprocess within the coverage level only by changing the multi-toneconfiguration.

That is, referring to FIG. 14 , when the terminal performs the randomaccess by selecting the 15 kHz multi-tone configuration of the initialCL1 and thereafter, consecutively unsuccessfully transmits the Msg3 ordoes not receive the contention resolution, the terminal attemptschanging the subcarrier configuration from the 15 kHz multi-toneconfiguration of the CL1 which is the same coverage level to the 15 kHzmulti-tone configuration without changing the coverage level.Thereafter, when the random access fails by the terminal, the terminalmay change the coverage level to the CL2 and thereafter, uses the 15 kHzmulti-tone configuration and when the random access fails by theterminal again, the terminal may attempt the random access by the 15 kHzsingle-tone configuration. When the random access fails by the terminalagain, the terminal may attempt the random access by the 3.75 kHzsingle-tone configuration of the CL3 last. In this case, in the casewhere the random access fails by the terminal, the terminal performs therandom access and thus, the number of preamble retransmission is morethan the maximum number of transmission due to unsuccessful Msg3 HARQtransmission or non-reception of the contention resolution message andthe case is defined to have the same meaning even in a description to bementioned below.

FIG. 15 is a schematic block diagram of an NB-IoT terminal according toan example embodiment of the present invention and FIG. 16 is aschematic block diagram of an NB-IoT communication system according toan example embodiment of the present invention.

Referring to FIGS. 15 and 16 , the NB-IoT terminal 100 is constituted bya transceiver 120, a processor 110, and an antenna 130 to performs therandom access method considering the random access procedure, thecoverage level for the uplink data transmission, and thesubcarrier-spacing and/or multi-tone configuration for the uplink datatransmission according to the example embodiments of the presentinvention described above with a base station 120.

The transceiver 120 transmits or receives a radio frequency signal to orfrom the base station 120 through an antenna 130, receives data and acontrol signal from the base station through the antenna 130 throughdownlink 152, and transmits the data and the control signal to the basestation 120 through uplink 154.

The processor 110 may determine the time of transmitting the controlsignal by controlling the transceiver 100. The processor 110 performsthe random access method considering the random access procedure, thecoverage level for the uplink data transmission, and the subcarrierspacing and/or multi-tone configuration according to the exampleembodiments of the present invention.

The machine communication terminal, for example, the NB-IoT terminal,the machine type communication (MTC) terminal, and a terminal inenhanced coverage may include the transceiver transmitting or receivingthe radio frequency signal to or from the base station through theantenna and the processor determining the time of transmitting the radiofrequency signal by controlling the transceiver. The processor processesa step of performing the random access process between the machinecommunication terminal and the base station and the random accessprocess may include a step of selecting the physical random accesschannel (PRACH) resource by considering the coverage level and whetherto support the multi-tone transmission or not. In detail, the radonaccess process may include the step of selecting the physical randomaccess channel (PRACH) resource by considering the coverage level andwhether to support the multi-tone transmission or not.

The machine communication device may include the transceivertransmitting or receiving the radio frequency signal to or from the basestation through the antenna and the processor determining the time oftransmitting the radio frequency signal by controlling the transceiver.The processor processes the step of performing the random access processbetween the machine communication terminal and the base station and therandom access process may include the step of selecting the physicalrandom access channel (PRACH) resource by considering the coverage leveland whether to support the multi-tone transmission or not. In detail,the radon access process may include the step of selecting the physicalrandom access channel (PRACH) resource by considering the coverage leveland whether to support the multi-tone transmission or not.

The processor 110 may be a universal processor, a special-purposeprocessor, a conventional processor, a digital signal processor (DSP), amicroprocessor, one or more microprocessors associated with a DSP core,a controller, a microcontroller, application specific integratedcircuits (ASICs), field programmable gate array (FPGA) circuits, anintegrated circuit (IC), a state machine, and the like. The processor110 may perform signal coding, data processing, power control,input/output processing, and/or predetermined other functions whichenable the terminal to operate a wireless environment. The processor 110may be coupled to the transceiver 120.

In FIG. 14 , the processor 110 and the transceiver 120 are illustratedas separate components, but the processor 110 and the transceiver 120may be integrated in an electronic package or chip together.

For example, in the example embodiment, the antenna 130 may be anantenna that is configured to transmit and/or receive RF signals. Inanother example embodiment, the antenna 130 may be, for example, aradiator/detector that is configured to transmit and/or receive IR, UV,or visible-ray signals. In yet another example embodiment, the antenna130 may be configured to transmit and receive both the RF signals andoptical signals. The antenna 130 may be configured to transmit and/orreceive a predetermined combination of the radio frequency signals. Thetransceiver 120 may be configured to modulate signals to be transmittedby the antenna 130 and demodulate signals received by the antenna 130.

The base station performing the random access process for the uplinkdata transmission with the cellular based machine communication terminalis constituted by the transceiver, the processor to perform may performthe random access method considering the random access procedure, thecoverage level for the uplink data transmission, and the subcarrierspacing and/or multi-tone configuration according to the exampleembodiments of the present invention described above with the NB-IoTterminal.

The base station performing the random access process for the uplinkdata transmission with the cellular based machine communication terminalmay include the transceiver transmitting or receiving the radiofrequency signal to or from the machine communication terminal throughthe antenna and the processor determining the time of transmitting theradio frequency signal by controlling the transceiver. The processorprocesses a step of receiving the random access preamble from themachine communication terminal, a step of transmitting the random accessresponse (RAR) message to the machine communication terminal, a step ofreceiving the message (Message 3) to request the connection for theuplink data transmission, and a step of transmitting the contentionresolution to announce that the Message which the machine communicationterminal transmits to the machine communication terminal is received bythe base station and the random access process may be implemented toconfigure the physical random access channel (PRACH) resource byconsidering the coverage level and the multi-tone configuration. Indetail, the radon access process may be implemented to configure thephysical random access channel (PRACH) resource by considering thecoverage level and the subcarrier spacing and/or multi-toneconfiguration.

The base station may communicate with one or more terminals through anair interface which a predetermined appropriate wireless communicationlink (for example, a radio frequency (RF), microwaves, infrared (IR),ultraviolet (UV), visible rays, and the like).

The NB-IoT communication system may become a multi-access system andadopt channel access schemes including CDMA, TDMA, FDMA, OFDMA, SC-FDMA,and the like. For example, the base station and the NB-IoT terminal ofthe RAN may implement a radio technology such as Universal MobileTelecommunications System (UMTS) terrestrial radio access (UTRA) capableof configuring the air interface by using wideband CDMA (WCDMA). TheWCDMA may include a communication protocol such as high-speed packetaccess (HSPA) and/or evolved HSPA (HSPA+). The HSPA may includeHigh-Speed Downlink Packet Access (HSDPA) and/or High-Speed UplinkPacket Access (HSUPA). In another example embodiment, the base stationand the MTC terminals may implement the radio technology such as evolvedUTRA (E-UTRA) capable of configuring the air interface by using LongTerm Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other example embodiments, the base station and the NB-IoT terminalmay implement radio technologies including IEEE 802.16 (that is,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA 2000 evolution-data optimized (EV-DO), interimstandard 2000 (IS-2000), interim standard 95 (IS-95), interim standard856 (IS-856), Global System for Mobile communications (GSM), EnhancedData rates for GSM Evolution (EDGE), GSM/EDGE RAN (GERAN), and the like.

The base station of FIG. 16 may be, for example, a wireless router, HNB,HeNB, or an AP and adopt a predetermined appropriate RAT which enablesradio access in a localized area such as places including business,home, vehicles, campuses, and the like. In the example embodiment, thebase station and the NB-IoT terminal may implement a radio technologysuch as IEEE 802.11 in order to configure a wireless local area network(WLAN). In another example embodiment, the base station and theterminals may implement a radio technology such as IEEE 802.15 in orderto configure a wireless personal local area network (WPLAN). In yetanother example embodiment, the base station and the NB-IoT terminalsmay use cellular based RATs (for example, WCDMA, CDMA2000, GSM, LTE,LTE-A, and the like) in order to configure a pico cell or a femto cell.The base station may directly access the Internet. Therefore, the basestation may not be required to access the Internet through a corenetwork.

FIG. 17 is a flowchart for describing a transmission request and atransmission process of small data according to an example embodiment ofthe present invention.

In FIG. 17 , the small data transmission request process is illustrated.The terminal transmits the random access (RA) request message (Msg1) inorder to perform the random access, and a type or an access cause of theRA request modified during such a process is expressed as ‘small datarequest’ and transmitted. The base station receives the request andthereafter, transmits the DCI in order to announce a resource totransmit the RA response (Msg2). Further, the base station determineswhether the resource for transmitting the small data may be allocated tothe corresponding terminal. Whether to support the small data may bedetermined by determining complexity of the random access resource forthe small data at the time of receiving the request. When the basestation may support transmission of the small data to the correspondingterminal, the base station transmits the RA response message (Msg2) byusing Small Data Radio Network Temporary Identifier (SD-RNTI)information which is newly defined instead of C-RNTI.

The terminal which is allocated with the SD-RNTI may thereafter performefficient data transmission through the small data transmission processof the present invention. In detail, during the small data transmissionprocess, the terminal transmits the Msg1 including data together theSD-RNTI, which is transmitted at the time of performing the randomaccess. The base station that receives the data through the RA request(Msg 1) may transmit an ACK to the corresponding terminal through thesubsequent DCI.

In the conventional data transmission scheme, the resource for uplinktransmission is acquired by performing the random access and thereafter,uplink data is transmitted and the DCI is received again to verifywhether the transmission is successful. The small data transmissionprocess of the present invention allows the Msg1 including the data tobe transmitted at the time of transmitting the Msg1 to reduce atransmission delay time and power consumption of the terminal. Such aprocess may be performed until the terminal may not maintain the SD-RNTIany longer and a termination criterion of the SD-RNTI may be defined asthe number of transmission, a transmission amount (bits), an allocationtime, and the like of the terminal in the network in advance andtransferred through the Msg2.

What is claimed is:
 1. A random access method for uplink datatransmission during a random access process, the random access methodperformed by the terminal, the method comprising: performing the randomaccess process between the cellular based machine communication terminaland the base station, wherein, in narrow band-Internet of Things(NB-IoT), which subcarrier spacing among 3.75 kHz and 15 kHz is used isindicated by using 1 bit in an uplink (UL) grant of a random accessresponse (RAR) message transmitted by the base station, wherein, inresponse to there being no subcarrier resource for a multi-tone MSG3transmission, a subcarrier for a single-tone MSG3 transmission is used,and the MSG3 is a message by which the terminal performs a connectionrequest to the base station for uplink data transmission, and wherein,in response to the terminal not receiving the RAR message, the terminaldetermines whether a number of preamble transmissions is more than amaximum number of preamble transmissions.
 2. The method of claim 1,wherein a physical random access channel (PRACH) resource is constitutedby a single-tone preamble numbered with 0, 1, . . . , (N_(sc)^(NPRACH)N_(MSG3) ^(NPRACH)−1) and a multi-tone preamble numbered with(N_(sc) ^(NPRACH)N_(MSG3) ^(NPRACH)), . . . , (N_(sc) ^(NPRACH)−1), andthe PRACH resource is defined as the following parameters transmittedfrom the base station the terminal: N_(period) ^(NPRACH)—NPRACH resourceperiodicity, N_(scoffset) ^(NPRACH)—frequency location of a firstsub-carrier allocated to NPRACH, N_(sc) ^(NPRACH)—a number ofsub-carriers allocated to NPRACH, N_(rep) ^(NPRACH)—a number of NPRACHrepetitions per attempt, N_(start) ^(NPRACH)—NPRACH starting time, andN_(MSG3) ^(NPRACH)—fraction for calculating a starting subcarrier indexfor a range of NPRACH subcarriers reserved for indication of userequipment (UE) support for multi-tone MSG3 transmission.
 3. The methodof claim 1, wherein, in response to a number of preamble transmissionsbeing more than a maximum number of preamble transmissions, a coveragelevel is changed and the number of preamble transmissions isinitialized.
 4. A random access method for uplink data transmissionduring a random access process, the random access method performed bythe terminal, the method comprising: performing the random accessprocess between the cellular based machine communication terminal andthe base station, wherein, in narrow band-Internet of Things (NB-IoT),which subcarrier spacing among 3.75 kHz and 15 kHz is used is indicatedby using 1 bit in an uplink (UL) grant of a random access response (RAR)message transmitted by the base station, wherein, when a random accesschannel (RACH) procedure is performed, the terminal divides thesubcarrier resources to be used in a physical random access channel(PRACH) according to a single-tone transmission or a multi-tonetransmission, and wherein, in response to a number of preambletransmissions being more than a maximum number of preambletransmissions, a coverage level is changed and the number of preambletransmissions is initialized.
 5. The method of claim 4, wherein, inresponse to there being no subcarrier resource for a multi-tone MSG3transmission, a subcarrier for a single-tone MSG3 transmission is used,and the MSG3 is a message by which the terminal performs a connectionrequest to the base station for uplink data transmission.
 6. The methodof claim 4, wherein a physical random access channel (PRACH) resource isconstituted by a single-tone preamble numbered with 0, 1, . . . ,(N_(sc) ^(NPRACH)N_(MSG3) ^(NPRACH)−1) and a multi-tone preamblenumbered with (N_(sc) ^(NPRACH)N_(MSG3) ^(NPRACH)), . . . , (N_(sc)^(NPRACH)−1), and the PRACH resource is defined as the followingparameters transmitted from the base station the terminal: N_(period)^(NPRACH)—NPRACH resource periodicity, N_(scoffset) ^(NPRACH)—frequencylocation of a first sub-carrier allocated to NPRACH, N_(sc) ^(NPRACH)—anumber of sub-carriers allocated to NPRACH, N_(rep) ^(NPRACH)—a numberof NPRACH repetitions per attempt, N_(start) ^(NPRACH)—NPRACH startingtime, and N_(MSG3) ^(NPRACH)—fraction for calculating a startingsubcarrier index for a range of NPRACH subcarriers reserved forindication of user equipment (UE) support for multi-tone MSG3transmission.
 7. The method of claim 6, wherein, in response to theterminal not receiving the RAR message, the terminal determines whethera number of preamble transmissions is more than a maximum number ofpreamble transmissions.
 8. A random access method for uplink datatransmission during a random access process, the random access methodperformed by the terminal, the method comprising: performing the randomaccess process between the cellular based machine communication terminaland the base station, wherein, in narrow band-Internet of Things(NB-IoT), which subcarrier spacing among 3.75 kHz and 15 kHz is used isindicated by using 1 bit in an uplink (UL) grant of a random accessresponse (RAR) message transmitted by the base station, wherein, when arandom access channel (RACH) procedure is performed, the terminaldivides the subcarrier resources to be used in a physical random accesschannel (PRACH) according to a single-tone transmission or a multi-tonetransmission, wherein, in response to the terminal not receiving the RARmessage, the terminal determines whether a number of preambletransmissions is more than a maximum number of preamble transmissions,and wherein, in response to there being no subcarrier resource for amulti-tone MSG3 transmission, a subcarrier for a single-tone MSG3transmission is used, and the MSG3 is a message by which the terminalperforms a connection request to the base station for uplink datatransmission.
 9. The method of claim 8, wherein a physical random accesschannel (PRACH) resource is constituted by a single-tone preamblenumbered with 0, 1, . . . , (N_(sc) ^(NPRACH)N_(MSG3) ^(NPRACH)−1) and amulti-tone preamble numbered with (N_(sc) ^(NPRACH)N_(MSG3) ^(NPRACH)),. . . , (N_(sc) ^(NPRACH)−1) and the PRACH resource is defined as thefollowing parameters transmitted from the base station the terminal:N_(period) ^(NPRACH)—NPRACH resource periodicity, N_(scoffset)^(NPRACH)—frequency location of a first sub-carrier allocated to NPRACH,N_(sc) ^(NPRACH)—a number of sub-carriers allocated to NPRACH, N_(rep)^(NPRACH)—a number of NPRACH repetitions per attempt, N_(start)^(NPRACH)—NPRACH starting time, and N_(MSG3) ^(NPRACH)—fraction forcalculating a starting subcarrier index for a range of NPRACHsubcarriers reserved for indication of user equipment (UE) support formulti-tone MSG3 transmission.
 10. The method of claim 8, wherein, inresponse to a number of preamble transmissions being more than a maximumnumber of preamble transmissions, a coverage level is changed and thenumber of preamble transmissions is initialized.